Field of the Invention
The present invention relates to a end panel, and to a container body or container provided by a double seam with such end panel.
Description of Related Art
Containers of the type according to the invention comprise an end panel that is connected to the container body via a double seam. A double seam is formed by first laying a panel edge against a body edge. In a first operation, the panel edge is curled radially outward over the body edge and then upwardly forming a curl and a transition wall of the double seam. Thereafter, the panel edge is urged to move radially inwardly until near or at the container body thereby forming the end hook. The body edge is thereby confined or closed into a panel loop formed by the panel edge, a curl and an adjacent part of the end panel. In a second operation, the panel loop is pushed against the container body whereby the panel edge becomes confined between the body edge and the container body. In the formed double seam the panel edge forms the end hook and the body edge forms the body hook of the double seam.
During the radial inward movement of the panel edge and to some extent also of the body edge the diameter in the curved section thereof will decrease. This decrease in diameter creates compression stresses in tangential directions in the metal material of the edges, that is, a direction along the circumference of the panel edge and the body edge. The compression stresses locally create defects in the metal and ultimately will result in pleats or wrinkles.
This phenomenon will be more pronounced when using thinner metal end panels and container bodies. A possible solution to the wrinkling phenomenon may be the formation of a double seam in which the end hook, and sometimes also the body hook, has a reduced length and thus extent to over a smaller distance into the double seam. Such double seam having a shorter end hook and possibly also a shorter body hook has a higher risk for leakage, particularly when the content of the closed container is (temporarily) pressurized. This internal pressure generates an internal splitting force on the container body and end panel and ultimately could unroll the double seam.
Wrinkling is an inherent problem in relation to double seams because the panel edge mandatorily has to move radially inwardly for forming the panel loop overlaying the body edge. Since the wrinkling problem will be more pronounced with thinner end panels and container bodies, it appears almost impossible to make a reliable double seam with thinner end panels and container bodies unless cost increasing additional measures are taken, such as compressing or pinching the double seam or use a sealing compound.
U.S. Pat. No. 2,455,737 disclosed a rectangular container provided with a rectangular closure. This closure is double seamed to a container body via a panel edge. The panel edge is provided in the curved sections of the panel edge with sharp V-shaped notches. The notches are so deep that the notch is also present in the transition wall between a curl of the panel wall and the end hook. The sharp V-shaped notches are dimensioned such that in the formed double seam the edges of the notch are brought in close contact, the notch is closed up and a continuous wall formed. This construction is intended to avoid leakage.
However, there remains a risk for leakage because the closing cannot be controlled so that the notch may not fully close. In addition, when over-closing the notch the edges do no longer abut, but overlap resulting in a circumferential stress and in an irregular “puckering” deformation interfering with the formation and tightness of the double seam. This is even more true when the notches are formed in a non-circular end panel because with different radii and/or straight edges, the compression stress and/or tensile stress is not substantially constant over the circumference.
In addition, the V-shaped notches have a sharp bottom end. Such sharp V-shape is prone to crack initiation due to stress, when the edge is curved radially outwardly and upwardly during the formation of the curl between the panel wall and the transition wall of the double seam.